Clutches are used to control the transmission of torque between rotatable shafts. Positive clutches, when engaged, lock the shafts together to rotate as one. Frictional clutches permit slipping between the shafts that allows different rotational velocities of the shafts, or when one shaft is locked, for the clutch to be used in a braking capacity.
It is known to produce electrical friction clutches in which a rotor, attached to one shaft, is sandwiched between a stationary electromagnet and an independently rotatable armature attached to a second shaft. Activation of the electromagnet produces a magnetic flux channeled through the material of the rotor and the armature drawing them together in frictional contact.
When high torque capacity is required, a multiple plate clutch may be used in which the two shafts are connected alternately to ones of interleaving disks arranged perpendicularly to the shafts. A compression of the disks together causes a transmission of torque in proportion to the compressing force and the number of disks. Larger numbers of disks permit higher torque transmission with less compressive force.
Typically the disks of a multiple plate clutch are compressed by mechanical or hydraulic means. Electrical activation of a multiple plate friction clutch is hampered by the inability to create a magnetic attraction between multiple plates analogous to the attraction of the armature and rotor in conventional electric friction clutch design.